This invention relates generally to telephony and more specifically to loop currents within telephone networks.
The use of modems and other data exchange equipment that utilize standard telephone lines and networks is increasing quickly in today""s society. This rapid growth in modem use is especially pronounced due to the introduction and incredible popularity of the Internet. Today, not only are the number of data communication sessions expanding, but the length of call hold times corresponding to these sessions is also increasing. The key difficulty with this utilization of telephone networks for data communications is that telephone systems, as structured thus far, are specifically designed to handle voice calls and the problems associated with voice communications. Therefore, as currently configured, transmission of modem communications within telephone lines has not been optimized.
There are numerous areas in which such data communications can be made more efficient. One such area is the amount of line current provided by the telephone company to the individual telephone lines during normal operation. Standard telephones require the line interface circuits to supply the power needed for the operation of the handsets. To accomplish this, telephone line interface circuits ensure that a current which is typically 50 mA at 52V is supplied to the telephone lines and therefore the individual handsets.
The key difference, with respect to dial-up modems, is their significantly reduced need for a high telephone line current. Generally, modems are locally powered and do not utilize the power being supplied through the telephone wires, making the large current unnecessary. A minimum line current is required in order to maintain a noise free connection and to sense for an xe2x80x9coff hookxe2x80x9d or xe2x80x9con hookxe2x80x9d condition, but a significantly reduced current from that required for standard telephone handsets will still allow modems to operate properly. In fact, modems would operate with reduced thermal dissipation if the line current being supplied to the modem was decreased during normal operations.
There exist telephone interfaces that operate with locally powered telephone handsets, such as Meridian Business System (MBS) telephones produced by Northern Telecom Limited of Montreal, Canada, that allow for the reduction in the line current in cases where the particular telephone handset does not require the full telephone line current. One example of an MBS telephone with this capability is MBS model number M5316. Unfortunately, this interface is specific to voice communications using telephone handsets with specially designed proprietary hardware. Also, dial-up modems are not utilized with the MBS telephones.
A system and procedure is thus needed that can reduce the telephone line current in cases that a modem or other data equipment session is initiated. Such a solution should be implemented without a significant increase in hardware or overall cost to the telephone network and without any changes to the modem hardware or software required. As well, preferably, such a network would detect the minimum current possible to maintain high quality communications and not allow the current to go below such a minimum level.
It is an object of the present invention to overcome the disadvantages of the prior art and, in particular, to provide an apparatus whereby telephone line current can be limited during data communications.
According to a first aspect, the present invention provides a control apparatus capable of being implemented within a line interface circuit coupled to a telephone station via a telephone line loop arranged to carry an ac current representative of voice or data and a dc current for powering a standard telephone handset, the control apparatus controlling operation of the line interface circuit by means of control logic operating within the control apparatus; and wherein the control logic operates to set the dc current on the telephone line loop to a predetermined first dc current level, to determine if the telephone station is of a first device type which requires less dc current on the telephone line loop than a standard telephone handset, and to set the dc current on the telephone line loop to a second lower dc current level if the telephone station is of the first device type.
According to a second aspect, the present invention provides a line interface circuit incorporating the control apparatus of the first aspect, the line interface circuit further comprising a communication apparatus for transmitting and receiving voice or data on the telephone line loop, a dc current detection apparatus for detecting the dc current on the telephone line loop, and a dc current adjustment apparatus for setting the dc current on the telephone line loop; and wherein the communication apparatus, the dc current detection apparatus, and the dc current adjustment apparatus are independently coupled between the telephone line loop and the control apparatus, and the control apparatus is coupled to an external apparatus.
According to a third aspect, the present invention provides in a control apparatus capable of being implemented within a line interface circuit coupled to a telephone station via a telephone line loop arranged to carry ac current representative of voice or data and a dc current for powering a standard telephone handset, a method of controlling the dc current on the telephone line loop, the method comprising the steps of: setting the dc current on the telephone line loop to a predetermined first dc current level; determining if the telephone station is of a first device type which requires less dc current on the telephone line loop than a standard telephone handset; and setting the dc current on the telephone line loop to a second lower dc current level if the telephone station is of the first device type.